28 June 2012

Visiting 35 bridges in 3 days certainly brings home the importance of good preparation. Here are some thoughts on what the dedicated Pontist planning a bridge tour ought to take with them.

Maps
As I discovered in Scotland, some of the finest bridges can be quite tricky to find. I visited two in private forests, far from the main road, and several which were down obscure footpaths, not always visible on street maps. A combination of different maps was invaluable. Google's satellite views and driving directions are helpful, but proper Ordnance Survey maps were essential to locate some of the bridges. For historic bridges in Scotland, the RCAHMS website has coordinates for bridges and links to good quality OS maps at various scales. It might have been useful to have GPS to locate some of the sites.

Google street view is also invaluable for "casing the joint", particularly in working out where to park. For one bridge, I parked in what turned out to be somebody's back garden, which wasn't ideal. The ability to make a quick getaway is also essential in getting through a long list of bridges ...

Camera equipment
My camera broke down on the second day of my trip, leaving me reliant on my mobile phone and my travelling companion's camera. Their camera was hampered by a lack of space on the memory card. So, take a good camera, take a spare camera, take spare memory cards etc. I travelled with a laptop, so I backed up photos at the end of each day.

As for what makes a good camera for bridge photography, a wide-angle lens and good low-light capability are helpful, but portability also matters, as does the risk that an expensive camera might get dunked in a river.

Research
There's a lot to be said for knowing as little as possible about a bridge before visiting it, so it can come as a surprise. But I've had many occasions where I've visited and photographed a bridge, then learned more about it later and discovered that I never even bothered to look at a key feature. For the Scottish bridge trip, I did my homework, and it definitely helped. It also turned up links to other bridges which I was unaware of but which turned out to be well worth visiting.

Advance research also included working out which bridges were publicly accessible, and which were on private land. Scotland has a broadly-based right to roam which allows access to large areas of private property, but not to all. This bridge trip involved crossing both farmyards and private gardens, neither of which are included in the right to roam. The right also only covers only non-motorised use - there's no right to park a car on private property. For two of the sites, I wrote to the landowners and sought permission in advance. I will try to flag up any access issues when I post the individual bridges here, but do your own research if you are considering visiting any of these places.

AccelerometerThis has to be the latest gadget in any Pontist's kit bag. My tool of choice was the Accelerometer Toy app for an Android phone, but there are other apps including ones for the iPhone. With this, you can record bridge vibrations, and use the data to determine natural frequencies and possibly even coefficients of damping.

Waterproof clothing
I'm sure there are some places where this isn't necessary, but in Scotland? In early summer? Absolutely vital. Waterproof clothing isn't just about being proof against water - it also guards against stinging nettles, scratches from clambering through bushes etc.

Walking stick
On the last day of the trip, I found an abandoned walking stick below one of the bridges. I wish I'd had it for the whole trip. To get to several bridges, and to gain good viewpoints for photography, it's often necessary to clamber down steep and unstable slopes, climb walls, perch precariously at a river's edge etc. The walking stick really helped, and I'll be carrying it on future bridge trips for certain.

On that point, several of the bridges I'll be covered are actually quite dangerous to approach, particularly when trying to find a good place to take a photo. I'll try and highlight particular cases, but at the risk of being highly patronising, be careful out there!

Machete and/or axe
I've mentioned above the need to scramble through bushes and other undergrowth to get to bridges and viewpoints. A machete might be ridiculous, but a strong stick does help beat a path through dense vegetation. At some bridges, almost impossible to photograph due to trees and bushes, I wished I had an axe to clear a better view.

A companion
This particular trip would have been far poorer without a travelling companion. A fellow Pontist can help with navigation, but also with safety. There were several places it would have been much riskier getting to if travelling alone.

I've recently returned from a tour of bridges in Scotland, mostly in the eastern Highlands. The trip took three days and visited 35 bridges. Over the next few weeks, I plan to feature every one of them here.

Some of them are bridges I've mentioned previously, but hopefully a fresh look at them will do no harm. Some are bridges I've been to before, but never covered here. A significant number were new to me, and almost certainly some of them will be new to most of you.

The raw numbers are 8 arch bridges, 9 girder bridge, 5 cable-stayed bridges, and 14 suspension bridges. There's no prize for spotting that those numbers don't add up to 35.

I'll be featuring bridges both ancient and modern, although mostly somewhere in between. Some are well-known, but several are particularly obscure, generally undeservedly so. Several of the bridges are among those in Britain which any serious Pontist should try and visit once in their life.

There are a few themes to look out for along the way.

First is "water". Unluckily, I chose the wettest weekend possible for the tour, so there was a lot of water under the bridges, as well as over, and as a result many of the photographs are far from the best.

Another theme is "eccentricity". Dividing the bridges into four classic typologies, like I did above, really doesn't do justice to most of these bridges. Several are unique, survivors of an age of experimentation, examples of design by trial-and-error rather than facsimiles of the last design to successfully roll off the computer production line.

Third comes "serviceability", particularly in relation to wobble. Quite a few of the bridges, even the most recently built, exhibit dynamic behaviour which goes well beyond what modern codes permit. Does this really matter? How important is individual context? Perhaps in 35 bridges time there may be some answers.

The last theme that leaps to mind is "immateriality". Several of the bridges slim down their material to an extent that I think any modern designer would find it impossible to match. One in particular almost seems to defy material science. These are a challenge to the contemporary engineer, something to marvel at and to aspire to.

Hopefully along the next 35 or so posts there will be something of interest to most of my readers. There will be a few thrills: bridges which are spectacular, and certainly a few in spectacular settings. Also a few spills, or at least cases where the Happy Pontist was very nearly spilled.

Okay, that's the introduction out of the way. The next post will expand a bit further on the logistics of the bridge tour, and then it will be on to the bridges themselves.

19 June 2012

The BBC report that £2.4m of funding has been agreed to repair Victoria Bridge in Bath, which I believe is the earliest of James Dredge's unusual suspension bridges to still be standing (picture copyright Pierre Terre). The bridge, which is Listed Grade II* due to its historic importance, was temporarily closed in 2010 following the discovery of cracks in some of the main metal members.

Works are expected to take place over 12 months starting in April 2013. Bath's report on the choice of refurbishment option makes interesting reading - the preferred solution is to take down most of the original wrought iron and replace it with a steel replica. While this isn't great in terms of retention of historic fabric, it is probably a sensible conclusion.

14 June 2012

An international ideas competition has been announced to try and find creative ways of re-using the redundant SR-520 Evergreen Point floating bridge (pictured, courtesy of pgsvensk), which currently crosses Lake Washington the east of Seattle. The state Department of Transport plans to replace the bridge with a higher-capacity structure in 2014.

The contest is independent of the bridge replacement project, and is aimed at the "design community" to see whether more creative uses can be found for the redundant bridge pontoons than the usual answers of breakwaters, floating docks etc. The contest is being promoted by Washington State University, and offers a first prize of US$3,000. There's no expectation of a design contract for any winning solution - this is purely an ideas competition.

The jury consists entirely of architects and related "design professionals", so don't expect any serious consideration of the technical feasibility of proposals submitted. It's primarily an opportunity for architects, artists and students to add to their portfolio.

Entries must be submitted by August 15th, and there is a small fee for registration.

08 June 2012

I gather some of the locals describe this as the "bridge to nowhere". It spans across Lady Herbert's Garden, landing in front of the Coventry Transport Museum. It carries pedestrians above a surviving remnant of Coventry's mediaeval city walls. However, it is undeniably fairly pointless, as you can quite easily walk around the wall at ground level, barely lengthening your journey.

The glass bridge is something of a Millennial folly, part of an ensemble of artistic projects intended to liven up the plaza area in front of the Transport Museum. The most prominent of these is the Whittle arch, a four-legged monument to jet engine pioneer Frank Whittle. This can be seen in the photo on the right.

The bridge, designed by Ramboll and fabricated by Rowecord, is 130m long in total, curving gently from the east before descending in a dramatic 15m diameter spiral ramp at its west end. Some 40m of the bridge is unsupported at this end, subject to substantial bending and torsional effects. These are resisted by a 762mm diameter hollow steel tube, which forms the primary structural member for the entire bridge. Vibrations are prevented by the presence of three tuned mass dampers inside the tube, although some movement is still quite perceptible.

The spiral ramp appears to be driven by the space available to achieve suitably shallow ramp gradients, rather than just the desire to make a bold structural statement. Aside from the main ramped route, there is a small staircase tucked away behind this part of the bridge, small, unwelcoming, and not one of the bridge's more successful elements.

Other than the spiral, the other unique feature of this bridge is its parapet, comprising extensive glass fins. Quite how these survive unbroken in a somewhat run-down city centre like Coventry's is a mystery to me. They are intended to reflect and scatter light when the bridge is illuminated at night - they don't form a functional part of the parapet restraint system. I think they are quite over-done, obtrusive both in size and in number.

Although it's all essentially unnecessary, the bridge does provide some nice views down into the gardens. It's hard not to think that a more minimalist balustrade would have been better in this respect as well, less distracting, and focussing attention on the views rather than shouting "look at me" quite so loudly.

For the most part, the bridge sits on slender columns with only a single small bearing at the top of each, something made possible by the significant plan curvature, which allows it to remain stable without the need for paired bearings. These can't be completely avoided however, as it otherwise lacks torsional stability, especially as it straightens out at one end.

The deck system comprises a series of anti-slip "planks" separated by grilles at frequent intervals. This serves a dual purpose: lighting is hidden below, and at night the deck lights up as a series of stripes, requiring no further illumination. It also allows the deck to drain freely, rather than having to capture surface water run-off at one end, which would be a challenge for such a long bridge. The downside is that the number of individual light fittings required is substantial, and also that a very visible pattern staining is produced on the main tube by the free-draining water.

Perhaps the oddest feature of the bridge is a weird cantilever wall which delineates the transition between the relatively straight section passing over the gardens, and the spiral curve over the Transport Museum piazza. I'm completely at a loss as to its purpose, but it not only looks odd from below, it completely blocks views off the bridge at this point. Can anyone explain it?

Overall, I admire the bridge's structural impudence, but find the parapets far too "busy", and wonder quite how much it must cost to maintain.